Re: So, what's the conversion process for an engine from Jet-A1 to Natural Gas?
To answer your first question, it may be almost that simple, the motor just needs the correct fuel/air mix to be pushed through the burners with the calorific value of the different fuels only affecting the consumption rate.
What you have next is a classic business case trade off situation.
The more you change on the motor converting it from an air blower to turning a genny the more efficient it becomes, the cheapest simplest fix is to literally bolt on a bigger gearbox & generator(Open cycle*), a full conversion has the turbine buried in a very complex heat exchanger & feedback loop to optimize the exhaust heat recovery (Closed cycle).
If the return on investment time for the efficient conversion doesn't beat the cheap (practically a bolt-on) solution during the expected wait time until grid connections can be made then we can all guess what's going to happen.
These converted jets won't go away in the long term either, they'll be kept as backup until the annual maintenance costs start to approach replacement cost by a more efficient system.
As for the Mercaptan issue (Sulfur), as long as the gas doesn't go wildly over the levels found in aviation kerosene the engines will operate.
* The exhaust heat (vast amounts) is lost.